1. Field of the Invention
The present invention relates to a radio relay apparatus periodically transmitting a beacon to a radio terminal apparatus, the radio terminal apparatus receiving the beacon from the radio relay apparatus, a method for these apparatuses, and a recording medium for these apparatuses.
2. Description of the Related Art
In recent years, the development of a radio communication system for building a radio network among a plurality of electronic devices to perform information communication has been advanced. In particular, the development of the field of a small-scale radio personal area network (PAN) having a communication range about a person has been advanced, and the radio PAN has been rapidly spread among people. The radio PAN has been realized by using, for example, ZigBee (registered trademark), which standardizes a physical layer and a media access control (MAC) layer in accordance with the IEEE 802.15 standard, and Bluetooth (registered trademark), which standardizes a physical layer and a MAC layer in accordance with the IEEE 802.15.1 standard.
ZigBee has been standardized by ZigBee Alliance, and uses the specifications of the IEEE 802.15.4 standard for the physical layer and the MAC layer. Consequently, ZigBee has the following features: having a speed lower than that of Bluetooth, but having a lower price, consuming lower power, being easily set up, and enabling a radio relay apparatus to be connected to many radio terminal apparatuses.
A radio communication system using ZigBee is composed of a radio relay apparatus and radio terminal apparatuses. A beacon mode is frequently used as the communication system of the radio communication system. By the beacon mode, a radio relay apparatus periodically transmits beacon signals at a predetermined period, and all of the radio terminal apparatuses receive the beacons, so that the radio terminal apparatuses perform radio communications with the radio relay apparatus in synchronization with the received beacons.
When the radio relay apparatus transmits data to a radio terminal apparatus, the radio relay apparatus stores the address of the radio terminal apparatus to which the data is transmitted in the pending addresses in beacons to transmit the data. Then the radio terminal apparatus that has received the beacons transmits a data request to the radio relay apparatus to receive the data if its own address exists in the beacons.
The number of the addresses of radio terminal apparatuses that can be stored in a pending address is defined by the IEEE 802.15.4 standard up to seven at a maximum in the radio communication system described above. Consequently, for example, even if data is transmitted to all of the radio terminal apparatuses in a radio communication system composed of one radio relay apparatus and many, e.g. eight or more, radio terminal apparatuses, seven addresses at a maximum can be stored in one beacon. Consequently, all of the radio terminal apparatuses perform their reception operations every transmission time of the beacons although only seven radio terminal apparatuses at a maximum can receive data at one transmission of a beacon. Consequently, because the radio terminal apparatuses perform the receptions of beacons even when the radio terminal apparatuses do not need to receive data, there is the problem of useless power consumption.